overview of recent atlas higgs physics...

Overview of recent ATLAS HiggsPhysics Results

Patricia Conde Muíño (LIP)Workshop on Multi-Higgs Models (5-9 Sept 2016)

2P. Conde Muíño Multi-Higgs workshop, 5-9 Sept 16

Summary of Run 1 results


Run 1 couplings combination

➢ Best ATLAS+CMS fit for the ratio of production modes and BR➢ Cancellation of inclusive production theoretical uncertainties➢ Reference channel: smallest systematics and overall uncertainty: H → ZZ➢


Run 1: Spin, Parity and mass

➢ JP SM assignment tested versus alternative hypothesis combining angular observables from H→gg, H→WW, H→ZZ channels

➢ Alternative hypothesis rejected at 99% CLs limit in favour of SM one


The LHC at 13 TeV

➢ Spectacular performance of the LHC this year

➢ 27.7 fb-1 delivered luminosity➢ 25.6 fb-1 recorded at ATLAS➢ Newest results use at most 13 fb-1 ➢ 91-98% of the collected data with good

quality for physics analysis

~13 fb-1 for summer results


ATLAS Run 2 Performance highlights

➢ Strong effort to understand the detector performance ➢ Some examples:

➢ Electron/muon reconstruction, trigger and identification efficiencies studied with data

➢ Differences data/MC corrected at analysis level

➢

➢

➢ Improved b-tagging efficiency➢ For 70% eff: ~400(10) rejection

on light (c) jets


Higgs re-discovery at 13 TeV

➢ H → ZZ → 4l➢ 14.8 fb-1 pp collisions @ 13 TeV

➢ H → gg ➢ 13.3 fb-1 pp collisions @ 13 TeV

ATLAS-CONF-2016-079 ATLAS-CONF-2016-067


Cross sections in H → gg & H → 4l

➢ Cross section as a function of the pp center of mass energy

➢ H → gg differential cross section as a funtion of p

T

gg ➢ Agreement with theory➢ Slightly harder pT in data

ATLAS-CONF-2016-081 ATLAS-CONF-2016-067


H→gg & H→4l combination @ 13TeV

➢ Fitted VBF and ggF contours➢ Dominant systematics:

➢ e/g energy resolution, g identification efficiency

➢ Theory: ggF acceptance in events with fixed number of jets

➢ Production cross sections assuming SM BR:

➢ Compatibility with SM: pSM

= 21%

ATLAS-CONF-2016-081


H → bb searches

➢ Explore non-dominant production modes➢ Vector boson fusion + photon (VBF search)

➢ Use photon to trigger➢ bbgjj non-resonant bckg. suppressed by ~10´

➢ Previous inclusive VBF (H→bb) limits:➢ ATLAS: obs/expect. upper limit : 4.4/5.4 ´ SM➢ CMS Run 1 obs/expect. upper limit: 5.5/2.5 ´ SM➢ CMS Run 2 (2015)

➢ obs/expect. upper limit: 3.0/5.0 ´ SM➢ Associated production with W or Z

(VH search)➢ Trigger on

e/m from ➢ W/Z decay➢

➢

WH: s = 1.373 pb ZH: s = 0.884 pb

VBF+g: s = 65.98 fb


WH and ZH with H → bb

0 lepton

➢ 3 channels: 0, 1, 2 leptons➢ 8 event categories

➢ 0/1/2 leptons, 2/3 (or ≥3) jets, pTV >/< 150 GeV

➢ BDT discriminant ➢ Profiled likelihood fit to measure signal strength

➢ Constraint main backgrounds

2 leptons1 lepton


Results H®bb in association with a W or Z

➢ Combined signal strength with 13.2 fb-1 of pp collisions at √s= 13 TeV

➢

➢

➢

➢ Systematic and statistical uncertainties of the same size

➢ Dominant systematics from b-tagging and background normalization & modelling (W+jets, Z+jets, top)

μVH , H → bb=0.21−0.50+0.51

➢ Fit cross checked with di-boson signal (WZ+ZZ with Z→bb)

➢ Observed significance: 3.2s μVZ=0.91±0.17(stat)−0.23

+0.32(sys)

ATLAS-CONF-2016-091


Search for H → bb in VBF+g production➢ Trigger:

➢ L1 trigger: single photon (pT > 25 GeV)

➢ High level trigger: 4 jets pT > 35 GeV, m

jj> 700 GeV

➢ Selection:➢ Tight ID photon, pT > 30 GeV

➢ 4 jets with pT> 40 GeV

➢ 2 central (|h| 80 GeV

➢ Non b-tagged jets: mjj> 800 GeV

➢ BDT discriminant➢ Built with variables uncorrelated to m

bb

➢

➢ Define 3 regions with different S/B➢ Fit m

bb in these 3 regions

Δ R( jet , γ) ,m jj ,Δη jj , H Tsoft , jet width ,γ centrality , pT

balance


H→bb VBF+g results ➢ Use a profile likelihood fit➢ Non resonant background estimated

with 2nd order polinomial fit in mbb

sideband

➢ Fit tested searching for Z®bb + g production: Expected 95% CL limit: Observed: 2.0

➢ Observed signal strength in the Higgs search:

➢ Expected 95% CL limit:➢

➢ Observed 95% CL limit:➢ 4´(s´BR)SM

➢

➢ High BDT score region➢ Low BDT score region:

μH ,VBF+γ=−3.9−2.7+2.8

1.8−0.5+0.7

ATLAS-CONF-2016-063

6.0−1.7+2.3


Search for Higgs boson in ttH production

➢ Many possible final states


Search for Higgs boson in ttH production

➢ Multi-leptons: cut and count in different event categories

➢ mgg in ttH (H→gg) leptonic events

➢ BDT discriminant in ttH (H→bb)


Results on ttH Higgs searches

➢ Combined signal strength:

➢ Expected and observed significance:

μ=1.7−0.5+0.5(stat )−0.6

+0.7(sys)


Search for the Higgs decays to muons

➢ Very rare decay in the SM but important to probe Yukawa coupling to second generation fermions

ATLAS-CONF-2016-041

19P. Conde Muíño ICHEP 2016

Beyond the Standard Model Searches

➢ High mass resonnances➢ CP odd Higgs: A→Zh→ llbb➢ Charged Higgs: H+→tn, H+→ tb


High mass neutral Higgs boson searches

➢ X → WW → ln ln ➢ X → gg ➢ X → ZZ → llnn

ggF

➢ X → Zg➢ X → ZZ → llqq

➢ X → ZZ → ll ll


High mass neutral Higgs boson searches

➢ X → WW → ln ln ➢ X → gg ➢ X → ZZ → llnn

ggF

➢ X → Zg➢ X → tt

➢ All searches compatible with SM background expectations



Limits on neutral high mass Higgs bosons

➢ Limits defined for different production modes in most cases

➢ X → Zg

AT

LA

S-C

ON

F-2

016-

044

AT

LA

S-C

ON

F-2

016-

056

➢ X → ZZ → llnn

ATLAS-CONF-2016-079

➢ X → WW → ln ln

AT

LA

S-C

ON

F-2

016-

074


➢ X → gg

ATLAS-CONF-2016-059

➢ X → tt

AT

LA

S-C

ON

F-2

016-

085


Search for a CP-odd Higgs A®Zh with h®bb

➢ Search for a CP-odd Higgs in gg fusion or bb production➢ Predicted by two Higgs doublet models➢ 3.2 fb-1 of pp collisions at √s = 13 TeV

➢ Two channels:➢ 2 leptons: A®Zh® llbb➢ 0 leptons: A®Zh®nnbb➢➢ h®bb reconstruction:➢ p

TZ < 500 GeV: Two calorimeter jets R=0.4

➢ pTZ > 500 GeV: boosted regime

➢ calorimeter jet R=1.0, trimmed ➢ b-tagging on track-jets R=0.2

➢ Search for a resonance in the invariant mass ➢ Use dedicated control regions for background

modelling

em control region


Results of the search for A®Zh with h®bb

➢ Profiled likelihood fit considering signal and control regions

➢ Dominant systematic uncertainties:➢ calibration/resolution of small-R and large-R

jets energy, large-R jets mass (high pT

Z), b-tagging efficiency and mistag rate

(2l only)

➢ 2lepton, 2 tag signal region


Charged Higgs search channels

➢ Decay channels➢ For m

H+> 200 GeV: tb final state dominate

➢ For mH+

< 200 GeV: tn decay dominates

➢ Production modes➢mH+

≤ mtop

mH+

> mtop

➢ Search channels➢ H+ → tb: 1 lepton, ≥4 jets (≥ 2 b-tags)

➢ H+→ tn: tau+ hadronic top decay

➢ Decay channels➢ For m

H+> 200 GeV: tb final state dominate

➢ For mH+

< 200 GeV: tn decay dominates

➢ Production modes➢


H+ → tn Search

➢ Discriminant: transverse mass


H+ → tn Search

➢ Observed 95% Cls limits on s´BR: ➢ 2. pb- 8 fb

➢ Exclusion in the hMSSM scenario➢ Significant improvements over

2015 results➢


H+ → bt

➢ Isolated lepton with pT › 25 GeV,

≥4 jets (≥2 b-tags)➢ 4 signal and 4 control regions➢ BDT discriminant ➢ Combined likelihood fit

➢ Constraint the backgrounds

Prefit Post-fit


H+ → bt results

➢ Observed 95% Cls limits on s´BR: ➢ 1.1 pb- 0.18 pb

➢ Exclusion in the mh

mod- MSSM benchmark model:

➢ Start to constraint high tan b


Search for HH production

➢ bbgg final state

ATLAS-CONF-2016-004

➢ bbbb final state

ATLAS-CONF-2016-049

➢ WWgg final state

ATLAS-CONF-2016-071


Limits on HH production➢ WWgg final state➢ bbbb final state

➢ bbgg final state


Summary and conclusions

➢ After the discovery of the Higgs boson in 2012, the ATLAS collaboration has focused on the study of its properties

➢ The Run 1 data at 7 and 8 TeV provided the first measurements, mainly in bosonic channels

➢ With around 13 fb-1 of 13 TeV pp collisions we have ➢ Re-discovered the Higgs boson in H → gg and H → ZZ → 4l final states➢ Searched for the Higgs decaying to b-quark pairs➢ Searched for associated production with top quark pairs➢ Search for new Higgs boson in a large variety of channels

➢ Reached sensitivity comparable/better than in Run 1➢ Given the current performance of the LHC, we expect improved and new

results in the future ➢

➢


Acknowledgements

➢ OE, FCT-Portugal, CERN/FIS-NUC/0005/2015


Backup


A → Zh with h→bb


Search for H/A → tt

➢ Redone Run 1 analysis considering interference effects between signal and background

➢ 6 different analysis categories➢ Limits in 2HDM: for m

A=500 GeV, tanb


Search for H/Z decaying to J/y g

2


Production cross sections of several processes


Search for new phenomena in H→gg + ET

miss

ATLAS-CONF-2016-087


Run 1 VH (H®bb) results

➢ Expected (observed) significance: 2.6 (1.6) for a mass of 125.36 GeV

μ=0.52±0.32(stat )±0.24(sys)


➢ Search for a CP-odd Higgs boson A →Zh→Zbb with 3.2 fb-1 of pp collisions at 13 TeV:


Di-photon resonance search

Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43

overview of recent atlas higgs physics...

Documents